Loud klunk !! when shifting into gear .... NP 203 belt?

Hello greeting's from the Pacific Northwest ,Ive got a 77 GMC Camper Special : I have a loud klunk when i shift into any gear . It has a turbo 350 in it and i took the front driveline off thinking it was a worn U-joint . But no . Ive checked the rear ring and pinion and there is very little play there !! So , this is where im stumped . Does the belt in the NP 203 strech ?? making this loud noise???
I can also hear it when im driving . let off the gas a little and it klunks , give it gas again and the same ...
Will it break if it is the belt and take out the whole transfer case ???

Well any input will be appriciated ....
Thanks , Tim
velzey@teleport.com

it's more than likely that it is play in your transfer case or loose splines on the rear drive shaft. You may want to pull the rear differential cover off while you have it up & check the teeth onthe ring gear & pinion.

no no no!!! Id bet money that its the front-axle ujoints.. put it in neutral, lock the hubs if you have em then turn the front driveshaft back and forth by hand and watch the axle ujoints very carefully..

My last truck was a '77 np203 truck and it did exactly what you described, very badly, and that was it.. luckily my current '77 np203 had the part time conversion installed in the t-case and the whole driveline is *tight*